Beam or truss arch constructions



March 1959 c. MACKINTOSH I BEAM OR muss ARCH CONSTRUCTIONS 2Sheets-Sheet 1 Filed Sept. 21. 1953 INVENTOR BY fiagm are y 9&2

ATTORNEYS March 3, 1959 c. MACKINTOSH BEAM OR muss ARCH CONSTRUCTIONSFiled Sept. 21. 1953 2 Sheets-Sheet 2 INVENTOR ATTORNEYS United StatesPatent BEAM 0R TRUSS ARCH CONSTRUCTIONS Charles Mackintosh, Los Angeles,Calif.

Application September 21, 1953, Serial No. 381,193 2 Claims. (Cl.108-23) This invention relates to improvements instructural spans.

More specifically it relates to a class of structure which I have chosento designate as a beam or truss arch in order to distinguish it fromconventional beam and truss structures which my invention is designed toreplace.

It has long been the practice in the structural field to use straight ortapered I beams (having upper and lower flange members joined by anintermediate solid web) to support loads of short span. Where a loadsupporting member is required having a relatively long span, a highover-all height is necessitated,'and it has been the practice to providetruss structures having upper and lower chords joined by intermediateweb members. Beam members have been found objectionable because of theirexcessive weight and reduced load handling capacity. Conventional trussstructures have also been found objectionable because secondary stressesare set up therein, in a number of cases greatly reducing the factor ofsafety for the structure. In addition, it has been necessary that thechord members of such trusses be heavy to compensate for the highbending moments inherent in such structure.

Accordingly it is an object of this invention to provide a structuralspan characterized by fixity of joints and heel eccentricities toeliminate all secondary stresses and accomplish a marked saving inmaterial because of reduced bending moments.

It is also an object of this invention to provide a span of thecharacter described which effects a marked saving in weight overconventional straight or tapered beam constructions.

I accomplish these objects by providing a structural span havinglongitudinally extending upper and lower unitary chord members and webmembers intermediate the chord ends. I fix the chord members together attheir heel ends eccentrically so that bending moments in the span areoffset by load tension in the lower chord to produce a condition ofnon-rotation at the ends of the upper chord. By placing the chord endsin a condition of non-rotation, bending moments are greatly reduced.Secondary stresses are eliminated by providing unitary chord members,the segmental portions of such chords being welded to one another sothat there is no rotation of segments about the welded joints.

It is another object of my invention to provide novel joist and hangermeans integral with my aforementioned truss or beam arch to insure thatthe arch is stayed against lateral bucking phenomena peculiar to saidtruss or beam arch.

These and further objects, features, and advantages will be apparentfrom the description which follows, read in connection with theaccompanying'drawings in which:

Figure 1 is a diagrammatic illustration of a well known type roof truss;

Figure 2 is a diagrammatic representation of one known type of beamsupport;

Figure 3 is a diagrammatic illustration of a second well known type rooftruss;

Patented Mar. 3, g

Figures 4 and 5 are diagrammatic illustrations of known type beamsupports;

In Figure 6 is shown a truss-arch type span which is one embodiment ofmy invention;

Figure 7 is a detail of the heel construction in my trussarch of Figure6;

Figure 8 is a beam-arch type span which is a second embodiment of myinvention; a

Figure 9 is a cross-sectional view through a roof construction employingthe principles of my invention and showing one embodiment of my improvedjoist hanger;

Figure 10 is a cross-sectional view taken along line 10-10 of Figure 9;

Figures 11, 12 and 13 are cross-sectional views through roofconstructions employing the principles of my invention and showingfurther embodiments of my improved joist hanger.

In order to facilitate an understanding of the invention, reference ismade to the embodiments thereof shown in the accompanying drawings anddetailed descriptive language is employed. It will nevertheless beunderstood that no limitation of the invention is thereby intended andthat various changes and alterations are contemplated such as wouldordinarily occur to one skilled in the art to which the inventionrelates.

Referring to the drawings, in Figure 1 is shown a well known type rooftruss having an upper chord- A--the segmental joints 18, 19 and 20 ofwhich lie upon a parabolic curve-and a lower chord B, between which arefixed intermediate web members 10, 11, 12 and 13. The upper chordcomprises four segments 14, 15, 16 and 17 pivotally fixed together atpin points 18, 19 and 20. At the heel ends of the truss the centerlinesof the upper and lower chords meet and are joined together at pin points21 and 22.

In the analysis of steel trusses, it is generally assumed that thejoints of the trusses are all pin joints. It is upon this assumptionthat all stress diagrams are drawn in order to determine the primarystress in each member of the truss. In order to actually get the samestresses as are computed in the analysis, many trusses, as in Figure l,have been built using pin connections as at 18, 19, 20, 21 and 22, inorder that each member so joined may rotate about the pin therebyreducing secondary bending stresses in the member, but inducing primarystresses which tend to carry a fixed uniform load in the upper chord. Insuch a truss each segment of the upper chord may be considered supportedat its ends as injthe case of segment 23 of Figure 2. Under uniformloading of segment 23 the maximum bending moment is at its center andcan be computed by the formula where W equals the uniform loading and Lequals the length of the segment.

Pin joints, as in the truss of Figure 1, are expensive and inconvenient.Thus, trusses are often built avoiding the use of pin connections, thesegments being fixed in their angular positions, but always thecenterlines of each of the joined members must intersect at a singlehinge point. This hinge location is the point at which a pin would belocated if pin connections were used. Belting at a plurality of pointsnear the joint has been resorted to, but joint continuity is absent atsuch junctures.

Recently welded segment connections have become popular, weldedconnections providing such complete continuity or unity of members thata segmental chord acts as a single unitary member rather than severalsegments.

Such a known truss is that roof type shown in Figure 3 with an upperchord C comprising segments 30, 31, 32 and 33 welded togetherandflhavinshinge .pointspfi,

35 and 36. A lower-chord D is provided together with intermediate webmembers 37, 33, 39 and 4t). The centerlines of the upper and lowerchords meet and are pivotall'y connected at theaheel ends 41 and 42. Insuch a welded structure the upper chord is a continuous unitary membersupported for angular movement at its ends similar to beam 23 in Figure2. The bending moment of the chord .at its apex 35is computed by theformula Unitary chord segments 30 and 31, therefore, are fully fixed bywelding at 35 so that this end 35 of the beam 30, 31 can neither movenor rotate. Such a fixed end beam is shown diagrammatically at 43 inFigure 4. At the center, corresponding to point'30 in Figure 3, of sucha beam .as 30 the bending moment is computed by the formula Attention isdirected'to Figure of the drawings Wherein is diagrammatically shown abeam member 44 fully fixed at both ends so that they can neither movenor rotate. A marked reduction in bending moments is achieved in a beamso supported. Under uniform load the moment at either end 45 or 46 ofsuch a structure may be computed by the following formula At the centerof a beam supported as in Figure 5, the bending "moment when the beam isunder uniform load is computed by the formula chord'member E comprisesfour segments Sti, 51, 52 and 53, the joints 54, 55 and 56 of which arewelded together so that upper chord E is a unitary member andindependent rotation of the segments about joints 54, 55 and 56 isimpossible. Because of this fixity of joints, secondary stresses, underuniform load on equal length segments, are largely eliminated. Webbingmembers 57, 58, 59, 6t 61 and 62 are fixed between the upper and lowerchords E and F as in the conventional roof-type truss.

In order that bending moments in the chords be reduced to the figurestypified by the beam with fully fixed ends of Figure 5, I have foundthat fixed ends in the upper load supporting chord may be obtained atthe heels --a and b of the span by producing a condition of no rotationat the heel joints, assuming the span to be under a uniform load. Iproduce this condition by introducing an eccentricity e into the heel ofthe truss. By eccentricity is meant forces not meeting at a point.Therefore, I provide a heel construction as shown in Figure 7 in whichthe centerlines 63 and 64 of upper and lower chords E and F,respectively, do not intersect, but fall short of intersecting at theheel ends by an eccentricity distance 6. The chord ends are welded to abutt plate 65, lower chord F being cut away and welded to the upperchord along 66 according to the designed angle :of inclination of chordE. A filler plate 67 is welded between chords E and 'F at theirjunction, and a heel plate 68 is welded to the lower chord F.

Taking the point 'c (Figure 7) on the centerline of the upper ch'ordmember E and assuming there is no loading upon the llowerchord member .Fexcept that of the negligible dead weight, it is seen that two momentsare present tending to produce rotation at 0. First, there is thedownwardly acting bending moment on E to the right of point c directedclockwise of c. Further, there is a moment counter-clockwise of c whichis produced by load tension in the lower chord F at a distance e frompoint C. This moment, therefore, tends to offset the bending moment onchord E to produce a condition of non-rotation at point 0. As waspointed out in connection with Figure 5, a beam having fully fixed ornonrotating end characteristics has a bending moment at its end equal toThus, to produce a condition of non-rotation in the upper chord at theheel of the span, it is necessary that the two moments about point 0 beequal and oppositely acting, or that where T equals the tension in lowerchord F, W equals the uniform loading on chord E, and L the length ofone of its segments. Therefore, the distance e may be calculated bysolving the following algebraic expression:

where M equals the bending moment taken from the end of the :lower chordF.

Thus in my arch type span shown in Figure 6, there will be negligiblestresses present in the web members 57, 58, 59, 6t}, 61 and 62. The onlypurpose such web members serve under conditions of balanced load is toact as hangers for the lower chord. In the event of unbalanced load, webmembers 58 and 61, which diverge upwardly of the lower chord, serve tominimize the tendency of peak joint 55 to rotate as they fix the :peakjoint in position, thereby greatly reducing the stresses inherent atunbalanced load.

Such a truss-arch structure as shown in Figure 6 is characterized bygreat economy, for the web members receive very little stress andconsequently their size and cable, tension of the member E beingemployed therein rather than that of the member F.

In Figure :8 is shown a second embodiment of my invention which isdesigned to replace vconventionalstraight or tapered beam constructions.

Accordingly, *I .call this embodiment a beam arch. This span comprisesanupper chord G and a lower chord H fixed together at their heel ends 1and j, eccentrically in the same manner as shown in Figure 7. Webmembers 70, 71, 72 and 73 are provided for joining the chord membersintermediate heel ends 1' and j. The upper chord comprises the segments74 and 75 welded together at their peak joint 76. The same formulae setout at (5) and (6) are applicable to determine the requiredeccentricity. It is important to note that web members 71 and 72 divergeupwardly from the lower chord to the upper chord, thereby absolutelyfixing joint 76 and prevening joint rotation even under unbalanced loadssuch as a load on 74 but not on 75. In the event that the beam arch ofFigure 8 is inverted so that chord H becomes the upper chord and chord Gbecomes the lower chord, it is necessary that webbing members 71 and 72be rearranged to diverge upwardly from chord G, thereby preventing thetendency of chord H to rotate about its center.

In known truss structures, as disclosed in Figures 1 and 3, having anupper chord fabricated from the conventional I-beam it is noteworthythat the lower flange of the chord is in a state of tension while theupper flange is in a state of compression. In order to prevent lateralbucking of the upper flange under compression, it has been the practiceto fix joist hangers to this flange for the reception of laterallyextending joists, there by staying the flange against lateral movement.

In my beam and arch constructions of Figures 6 and 8 it is to be notedthat compression is produced in the lower flange of the upper chord.Thus, it becomes necessary that the lower flange, as well as the upperflange, be stayed against lateral bucking. I prevent such bucking byproviding a joist hanger which is welded to both the upper and lowerflanges. Wood joists may then be fixed within the hangers to stay thechord flanges against undesirable bucking.

Several embodiments of my improved joist hanger construction are set outin Figures 9 through 12.

In Figures 9 and 10 is shown a two-part hanger comprising joistconfining members 80 and 81 welded together at 82, and to the upperchord K of a span constructed according to the teachings of my inventionat points 83, 84, and 85. Member 80 and portion 81a of member 81 extendgenerally transverse to upper chord K, portion 81b of member 81extending longitudinally of chord K to act as a joist seat. At theopposite side of the chord K an identical hanger L is welded as may beseen in Figure 10. A wood joist 86 is placed in the hanger and securedtherein by boltsor nails 87 and 88. As may be seen in Figure 10, thehanger member 80 has apertures for reception of the securing nails, theupper aperture 89 preferably being slotted vertically to compensate forshrinking or expansion of the wood joist. The joist seat portion of thehanger is dimensioned to such a depth that the joist 86 will projectslightly above the upper flange 90 of upper chord K. In such a manner,diagonal roof sheathing 91, or the like, may be nailed directly to thejoist and the necessity for fixing blocking to upper flange 90 of chordmember K is thereby eliminated.

In Figure 11 is shown a three-part hanger welded to an upper chord K andcomprising members 92, 93 and 94. Members 92 and 93 are welded at 95,seat member 94 being welded between members 92 and 93. Nail aperturesare formed in member 92 in the same manner as shown in Figure 10.

Figures 12 and 13 show a one-piece hanger welded to an upper chord K,the member 96 having nail receiving apertures similar to those in Figure10 for fixing the joist 97. therein, while the member 98 has a joistreceiving slot at its base for receiving a joist snugly therein. Thenecessity for nail or bolt apertures in hanger 98 is thereby eliminated.

The truss and beam arch constructions illustrated and described aboveare by way of example only, and any changes which might occur to oneskilled in the art are contemplated by the present invention, within thescope of the following claims.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. In a structural span, a longitudinally extending upper chord membercomprising a plurality of segments which intersect upon a conic sectionand are fixed to gether by welding, a lowerunitary chord member, webmembers fixed between said chord members intermediate the ends thereof,said chord members being fixed together at their ends and having theircenter lines at such ends spaced apart a distance e determined by theformula where W is the load uniformly applied on the upper chord, L isthe moment arm for the load W, and T is the load tension in the lowerchord, whereby the bending moments in the span upon the application of adownwardly acting load to the upper chord are substantially ofi-set by aload tension in the lower chord to produce a condition of substantialnon-rotation in the upper chord ends.

2. In a structural span, a longitudinally extending upper chord membercomprising a plurality of segments which intersect upon a conic sectionand are fixed together by welding, a lower unitary chord member, webmembers fixed between said chord members intermediate the ends thereofand diverging upwardly from said lower chord and outwardly of the centerof the span to prevent rotation of the upper chord about its center,said chord members being fixed together at their ends and having theircenter lines at such ends spaced apart a distance e determined by theformula where W is the load uniformly applied on the upper chord, L isthe moment arm for the load W, and T is the load tension in the lowerchord, whereby the bending moments in the span upon the application of adownwardly acting load to the upper chord are substantially ofi-set by aload tension in the lower chord to produce a condition of substantialnon-rotation in the upper chord ends.

References Cited in the file of this patent UNITED STATES PATENTS770,050 Dreyer Sept. 13, 1904 796,433 Kahn Aug. 8, 1905 1,097,934 PriceMay 26, 1914 1,552,777 Trachte -e Sept. 8, 1925 1,678,738 Macomber July31, 1928 2,642,825 McElhone June 23, 1953 FOREIGN PATENTS 549,051 GreatBritain of 1942

